As unnerving as it sounds, the technology could eventually have beneficial real-world applications

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A bicyclist passes the gay liberation sculpture along Lomita Mall at Stanford University. Buried on the campus are three miles of fiber optic cables that are now being used to detect movement above ground in a research project called the Big Glass Microphone. (Gary Reyes/ Bay Area News Group)

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It’s part of a project called the Big Glass Microphone, aimed at demonstrating just what a three-mile stretch of underground cables can detect. And now that researchers know that fiber optics can be used to sense human movement, they’re wondering whether it points to a future of surveillance without the need for fancy cameras and other technology.

As unnerving as it sounds, the technology could eventually have beneficial real-world applications — such as quickly identifying a car whose driver is endangering lives by going 50 mph over the speed limit, or revealing the source of sounds that may be messing up science experiments on campus.

“The whole world is getting to the point where it’s beginning to be wired up as a whole sensor network. It’s picking up all kinds of information incidentally,” said Jon Christensen, an adjunct assistant professor at UCLA and partner and strategic adviser at Stamen Design.

Stamen, a San Francisco-based visualization and data communication company, is collaborating on the project with Stanford’s geophysics department; OptaSense, an international acoustic-sensing company; and the Victoria and Albert Museum in London.

The project has created an online animation of the vibrations picked up by the fiber optic cable — which has been continuously recording noises since last September.

Fiber optic cables are found all over the world, from the bottom of oceans to beneath our sidewalks. They’re thin strands of glass that take a piece of information, such as a person’s voice, and temporarily turn it into light to send it to its destination.

The cables allow you to instantaneously send photos halfway around the world, but they can also tell you how heavy the traffic is on the main drag in your hometown.

And it turns out if you know what to listen to, the fiber optic cables can reveal a whole lot more.

Eileen Martin, a Stanford Ph.D. student in computational and mathematical engineering, is working on an experiment in which her team sets off tiny controlled explosions and then records them using a fiber optic cable network beneath the ground. (Photo by Jean Martin)

Usually, researchers ignore any incidental extra signals that the cables pick up — those that don’t have to do with the cables’ main purpose — and filter them out as “noise.”

But vibrations can cause these hair-thin strands to stretch. By measuring the amount they stretch, researchers can discern if a person, car or a motorcycle is rolling past it.

The fiber optic loop under Stanford’s campus was originally installed last August for seismic research, but the Stanford team, with the help of OptaSense, decided to turn the noise into signals.

Eileen Martin is a Stanford Ph.D. student in computational and mathematical engineering working on analyzing seismic research from the campus cables. She uses them to detect earth-rumbling events as small as explosions from quarry blasts in Cupertino to the large earthquake in Oklahoma last September. Martin doesn’t filter out the noise, but uses it to figure out how noisy the Stanford campus is in order to determine how stable the ground is.

Human ears can’t hear most of this noise.

“Think a couple of octaves below the lowest point on a piano, and that’s where the kind of frequency range is where all these noises happen,” she said.

The Stamen team says the project raises all kinds of questions about privacy.

“Infrastructure is listening to us … but how much do we want our infrastructure to be monitoring us at the same time that we’re monitoring it?” Christensen asked.

Eric Rodenbeck, the founder and CEO of Stamen, thinks fiber optic cables will eventually be able to tell the difference between different models of cars and how many people are riding in them.

According to Rodenbeck, each kind of car has a unique signature depending on its make and its load weight, which registers as the mechanical vibrations of the engine as the car goes by. This in turn vibrates the fiber optic cables in varying frequencies.

“When we start talking about smart cities and digital infrastructure … we are pointing to a future where there’s not just sensors everywhere, but the whole world and all of the infrastructure in it can be used as a sensor,” Rodenbeck said. “What does privacy even mean when every place you go your individual gait is trackable or the specific weight of your car is trackable?”

The Stamen team thinks even buildings can be used as sensors in the same way to pick up slight vibrations.

“A building and the wires and other infrastructure in it could vibrate if a person is walking by,” Christensen said, “and you could pick it up if you’re listening closely enough.”

No doubt, Big Brother would be thrilled. But some people might argue that the potential benefits outweigh the privacy concerns.

“We can learn very useful things,” Christensen said. “Is a pipeline leaking? Is a building sealed to be energy efficient? Is the flow of traffic optimal on this road?”

And it could eliminate having to install layers of security cameras and other expensive technology.

“Basically this sensing ability just falls off the truck,” Christensen said. “You kind of get it for free once you have a fiber optic cable and a box at the end of it.”

Chimed in Rodenbeck: “We have a worldwide sensing network — and you have that without satellites, and you have that without cameras. What other kinds of things can be used as listening devices?”

​Yasemin Saplakoglu, a science-writing intern at the Mercury News, is a graduate student in the Science Communication Program at UC Santa Cruz. She holds a bachelor's degree in biomedical engineering from the University of Connecticut.

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